KCSE CHEMISTRY QUESTIONS AND ANSWERS PER TOPIC
The table below gives the solubility’s of substances T and U at 10°C and 40°C.
When an aqueous mixture containing 55g of T and 12g of U at 80°c was cooled to 10°c, crystals formed.
a) Identify the crystals formed b) Determined the mass of the crystals formed c) Name the method used to obtain the crystals
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Aqueous hydrogen chloride reacts with potassium manganate (VII) to produce chlorine gas, while a solution of hydrogen chloride in methylbenzene has no effect
on potassium manganate (VII). Explain this observation
Draw a labeled diagram to illustrate how alpha, beta and gamma radiations can be distinguished from each other.
Describe a simple laboratory experiment that can be sued to distinguish between sodium and sulphide and sodium carbonate.
Expected Answer
Add dilute acid (e.g. HCI or H2SO4) to each substances separately. If Na2S, colourless gas, smell of rotten eggs
(a) A student electroplated a spoon with copper metal .Write an equation for the process that took place at the cathode.
(b) Calculate the time in minutes required to deposit 1.184g of copper if a current of 2 amperes was used. (1 Faraday = 96500 coulombs, Cu=63.5).
The flow chart below shows a sequence of reactions involving a mixture of two salts, mixture M. Study it and answer the questions that follow.
a) Write the formula of the following;
i) anion in solid Q ii) the two salts present in mixture M. b) Write an ionic equation for the reaction in step (VI) c) State and explain the observations made in step (V). d) i) Starting with Lead (II) oxide, describe how a pure solid sample of lead sulphate can be prepared in the laboratory. ii) How can one determine whether the lead sulphate prepared is pure?
ANSWERS
(c)The solution changes from blue to colourless and a brown solid is formed.
The magnesium which is above copper in the reactivity series displaces the copper ions from the solution. Apparatus become warm. The reaction is exothermic. (d)(i) Add nitric (V) acid to lead oxide, filter add a soluble sulphate/ sulphuric acid to the filtrate . Filter and wash residue with distilled water to remove traces of the filtrate, then dry residue between i. filter papers /oven. (ii) Determine the melting point, if it is pure the melting point will be constant.
a) The set up below was used to investigate the products formed at electrodes during electrolysis of aqueous magnesium sulphate using inert electrodes. Use it to answer the questions that follow.
i) During the electrolysis, hydrogen gas was formed at electrode Y. identify the anode. Give a reason for your answer.
ii) Write the equation for the reaction with takes place at electrode X. iii) Why is the concentration of magnesium sulphate expected to increase during electrolysis? iv) What will be observed if red and blue litmus papers were dipped into the solution after electrolysis? b) During electrolysis of magnesium sulphate, a current of 0.3A was passed for 30 minutes. Calculate the volume of gas produced at the anode.(Molar gas volume = 24dm3; 1 Faraday = 96,500C.). c) State two applications of electrolysis.
The factors which affect the rate of reaction between lead carbonate and dilute nitric (V) acid were investigated by carrying out three experiments;
a) Other than concentration , name the factor that was investigated in the experiments.
b) For each experiment, the same volume of acid (excess) and mass of lead carbonate were used and the volume of gas liberated measured with time. i) Draw a set up that can be used to investigate the rate of reaction for one of the experiments. ii) On the grid provided, sketch the curves obtained when the volume of gas produced was plotted against time for each of the three experiments and label each as 1, 2 or 3.
iii) Write an equation for the reaction that took place.
c) If the experiments were carried out using dilute hydrochloric acid in place of dilute nitric (V) acid, the reaction would start, slow down and eventually stop. Explain these observations. d) A solution of bromine gas in water is an example of a chemical reaction in a state of balance. The reaction involved is represented by the equation below.
State and explain the observation made when hydrochloric acid is added to the mixture at equilibrium.
a) Draw the structural formula for all the isomers of C2H3CL3
b) Describe two chemical tests that can be used to distinguish between ethane and ethane. c) The following scheme represents various reactions starting with propan-1-ol. Use it to answer the questions that follow.
i) Name one substance that can be used in step I.
ii) Give the general formula of X. iii) Write the equation for the reaction in step IV. iv) Calculate the mass of propan-I-ol which when burnt completely in air at room temperature and pressure would produce 18dm3 of gas. (C = 12.0; O = 16.0; H = 1.0; Molar gas volume = 24dm3)
ANSWERS
At 298K and 1 atmosphere, graphite changes into diamond according to the equation:
In the space provided, sketch a simple energy level diagram for the above change.
Sample solutions of salt were labeled as I,II, III and IV. The actual solutions, not in that order are lead nitrate, zinc sulphate potassium chloride and calcium chloride.
The apparatus shown in the diagram below were used to investigate the products formed when concentrated sodium chloride was electrolysed using inert electrodes.
(a) Write the equation for the reaction that takes place at electrode A.
(b) If the concentrated sodium chloride was replaced with dilute sodium chloride, what product would be formed at electrode A? Explain.
Describe two chemical tests that can be used to distinguish ethanol from ethanoic acid.
Aluminium is both malleable and ductile,
(a) What is meant by? (i) malleable; (ii) ductible. (b) State one use of aluminium based on: (i) malleability (ii) ductility
ANSWERS
(a) (i) Malleable - Can be hammed into sheets
(ii) Ductile - Can be drawn into wires (b) (i) Saucepans (ii) Electrical transmission lines
Give two uses of the polymer polystyrene.
ANSWERS
In an experiment, 0.8gm of magnesium of powder were reacted with excess dilute sulphuric acid at 250C . The time for the reaction to come to completion was recorded. The experiment was repeated at 400C. In which experiment was the time taken shorter? Explain your answer.
Expected Response
Experiment II. At a high temperature the particles have more energy, hence rate of high energy collisions increase.
Study the nuclear reaction given below and answer the questions that follow
Study the energy level diagram below and answer the questions that follow.
(a) Give the name of ΔHA
(b) How can ΔHB be reduced? Give a reason.
ANSWERS
(a) Heat of reaction
(b) Using a catalyst Catalyst reduce activation energy.
Below is a representation of an electrochemical cell.
Calculate the E.M.F of the electrochemical cell.
A dynamic equilibrium is established when hydrogen and carbon (IV) oxide react as shown below:
What is the effect of adding powdered iron catalyst on the position of the equilibrium?
Give a reason.
ANSWERS
(a) A student was supplied with a colourless liquid suspected to be water
The flow chart below shows the various stages of water treatment. Study it and answer the questions that follow
II Addition of sodium hypochlorite (c) It was confirmed that magnesium sulphate was present in the tap water
(a) Give the names of the following compounds
Name the type of bromination reaction that takes place in: (i) and (ii)
(d) The polymerization of tetra flouroathene (C2H4) is similar to that of ethane ( C2H4)
(e) State any two advantages that synthetic polymers have over natural polymers
​The flow chart below illustrate the industrial extraction of lead metal. Study it and answer the questions that follow
(a)
(c) State one use of lead other than the making of lead pipes Related Chemistry Questions and Answers on Metals Form 4 Level
1 (a) The diagram below represents a mercury cell that can be used in the industrial manufacture of sodium hydroxide. Study it and answer the question that follow
Hydrogen and fluorine react according to the equation below
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